Yes, they'd just be part of the random races when you hire anywhere else. The Ryn won't get a homeworld (they don't really have one canonly), so you'll never be able to specifically hire a multitude of them.

This relates to the homeworlds of new races so I will ask it here::
How does one discover the hidden races? Do you have to descend to the surface of a planet? Could they be found in any terrain or should we look for cities only?
Or is it enough if you find the system they are in?
Thank you.

I'd presume that it would be linked with the finding of hidden systems, so once you find one it then triggers the choosing of that race. Whether it is immediate or you have to wait the 7 days I don't know.